西部铁角蕨 xi bu tie jiao jue

Asplenium atuntzeense Viane & Reichstein; A. daghestanicum Christ subsp. aitchisonii (Fraser-Jenkins & Reichstein) Fraser-Jenkins; A. minutum Chang Y. Yang (1993), not Willdenow ex Klotsch (1847); A. subdigitatum Ching (1985), not Mettenius ex Kuhn (1868); A. xinjiangense Ching.

Plants 8-18 cm tall. Rhizome short, erect to ascending, apex scaly; scales dark brown, ovate-triangular, 2-4 mm, often with marginal fimbriae. Fronds caespitose, bright to dark green, (2-)7-11(-15) cm; stipe usually as long as (up to 1/3 of) lamina, 2-6 cm, semiterete, base dark brown for 2-15 mm but green toward rachis, with narrow scales and uniseriate hairs, subglabrous when old; lamina narrowly triangular to ovate, base widest, (2-)3-6 × (0.5-)1-2(-3) cm, bipinnate at base, apex acute; pinnae 5-10 pairs, subopposite or alternate, basal pinnae with short stalks 0.5-2(-3) mm, upper pinnae sessile, basal pinnae usually largest, triangular to deltoid, 3-12(-18) × 3-10(-15) mm, apex obtuse, lowest pinnae 0.5-2 cm apart, each usually with 2 pinnules and broad, deeply pinnatifid apex, upper pinnae smaller, less divided and entire near apex; ultimate segments with cuneiform base and obtuse apex, margin dentate, with 3-5(-7) spreading teeth. Costa obvious but veins obscure, veins anadromously branching. Frond herbaceous, green to brown-green when dried, rachis semiterete, green, with narrow scales and uniseriate hairs; average guard cell length 56-61 µm. Sori submedian to median on subtending vein, confluent when mature, 2-3 mm; indusia membranous, repand to entire, opening toward costule or toward costa. Spores with lophate (costate to cristate) perispore, average exospore length 38-42 µm. Sexual hexaploid species: 2n = 216.

On half-shaded, non-calcareous rocks; 1700-4200 m. S Gansu, Sichuan, Xinjiang, Xizang, Yunnan [Bhutan, N India, Nepal, Pakistan].

Asplenium aitchisonii is similar to other members of the A. varians complex (i.e., A. altajense, A. kukkonenii, A. semivarians, A. tenuicaule, A. varians) and was often included in A. varians, e.g., by Beddome (Handb. Ferns Brit. India, 158. 1883), Hope (J. Bombay Nat. Hist. Soc. 13: 667. 1901), Stewart (Biologia 3: 133-164. 1957), and Stewart in Nasir and Ali (Fl. W. Pakistan, 18. 1972); however, it is usually widest at the base and has longer stomata and spores due to its higher number of chromosomes. This is an allohexaploid (not an octoploid as stated in the original description). Asplenium daghestanicum Christ, a tetraploid from the Caucasus and Libya (Tibesti), is genetically isolated from this species and thus better kept as a separate species. Plants from isolated populations, growing in sheltered conditions in regions with an extreme climate, are often less developed and have been described as separate species (i.e., A. xinjiangense, A. subdigitatum, A. minutum).